Device for the supervision of a treatment in an enclosure at very low pressure

ABSTRACT

A device for supervising a thermal treatment operation taking place inside a vacuum enclosure by detecting and/or measuring emitted radiation accompanying the operation comprises a compartment maintained at a higher pressure substantially closed at one end by a partition located inside the enclosure and having an opening for passing radiation from the enclosure to a radiation sensitive element closing the compartment at its other end, the size of the opening and the distance between the partition and the radiation sensitive element being such that, for the value of the pressure in the compartment, substantially no vapor molecules originating from the enclosure during the operation reach the sensitive element. The operation may for example comprise an electron gun bombarding a weld region within the enclosure.

United States Patent [72] Inventors Bernard M. Daigne Malakoff; Louis Pelletier, Sainte-Genevieve Des Bois, France [21] Appl. No. 713,921

[22] Filed Mar. 18, 1968 [45] Patented May 25, 1971 Office National DEtudes Et De Recherches Aerospatiales (par abreviation O.N.E.R.A.)

[73] Assignee [32] Priority Mar. 21,1967 [33] France [31 99648 [54] DEVICE FOR THE SUPERVISION OF A TREATMENT IN AN ENCLOSURE AT VERY LOW (8), 49.5 (0), 51.5, 83.3 IR; 73/355; 219/121 (EB) [56] Reierences Cited UNITED STATES PATENTS 3,346,736 10/1967 Neuhaus 250/49.5(8)

Primary Examiner-James W. Lawrence Assistant ExaminerA. L. Birch Attorney-Strauch, Nolan, Neale, Nies and Kurz ABSTRACT: A device for supervising a thermal treatment operation taking place inside a vacuum enclosure by detecting and/or measuring emitted radiation accompanying the operation comprises a compartment maintained at a higher pressure substantially closed at one end by a partition located inside the enclosure and having an opening for passing radiation from the enclosure to a radiation sensitive element closing the compartment at its other end, the size of the opening and the distance between the partition and the radiation sensitive element being such that, for the value of the pressure in the compartment, substantially no vapor molecules originating from the enclosure during the operation reach the sensitive element. The operation may for example comprise an electron gun bombarding a weld region within the enclosure.

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DEVllCE lFOR THE SUPERVISION OF A TREATMENT IN AN ENCLOSURE AT VERY LOW PRESSURE The invention relates to a device for supervising a thermal treatment operation taking place in an enclosure space at a very low pressure by using radiation accompanying the operation.

The device may be used to advantage in installations comprising an enclosure in which a high vacuum prevails or is maintained, although the atmosphere of the enclosure may contain a condensable vapor such as that which is given off by a metal in the liquid state contained in the enclosure.

When it is desired to make observations in such installations, a transparent portion or porthole is normally provided in the wall of the enclosure. But the conditions for the transmission of the radiation through the porthole are constantly modified by the deposit which occurs thereon in such a manner that the radiation produced inside the enclosure is more or less absorbed by the porthole and it is difficult, if not impossible, to monitor effectively the course of the internal operations.

In addition, even for limited supervision, such as that effected in the visible spectrum by direct observation with the naked eye, or by means of optical instruments, it is necessary to provide relatively complicated means in order to keep the porthole sufficiently transparent.

it has been proposed, for example, that a rotating slotted disc should be placed in front of the porthole but the deposit is only slowed down by this and not eliminated and the construe tion is complicated and expensive.

According to another proposal, a transparent shield which is changed periodically is placed in front of the porthole. Such an arrangement cannot be used for prolonged treatments and necessitates difficult manipulation.

It has also been proposed that scavenging by means of a gas should be effected inside the enclosure in the vicinity of the porthole in order to counteract the arrival of the molecules of metal vapor on the inside face of the porthole. But the admission of the scavenging gas is such that it is difficult, if not impossible, to maintain the pressure in the enclosure at the low value required even if the pumping means are developed considerably.

it has also been proposed that a compartment, the outside face of which consists of a porthole and the inside face of which, separating it from the enclosure, comprises an aperture of relatively large section to permit direct observation, should be fitted to the wall of the enclosure, at the outside thereof; A gas at a sufficient pressure to oppose the incidence of vapor molecules on the porthole is admitted into said compartment but this gas tends to cause the pressure inside the enclosure to rise excessively because of the relatively large section of the aperture permitting observation. The result may be the necessity of increasing to a considerable extent the power of the pumping means necessary to maintain the vacuum required inside the enclosure.

in any case, none of the means proposed ensures a constant transmission power for the porthole.

in such installations, therefore, continuous measurements of radiant energy, whether thermal, luminous or otherwise, with the required fidelity, are out of the question.

it is an object of the invention to provide a device which overcomes these disadvantages.

it is a particular object of the invention to provide a device which, despite being in communication with the enclosure, places a member or element which is sensitive to the radiation under such conditions that its operation is not adversely affected by the condensable vapors or the corrosive vapors which the atmosphere of the enclosure may contain.

in this respect, it is an object of the invention to provide a protection device for a sensitive element which will be absolutely transparent to all forms of electromagnetic or corpuscular radiation which may have to be measured in the course of a treatment under vacuum.

It is likewise an object of the invention to provide such a device the presence of which does not necessitate any increase in the power of the pumping means provided to maintain the required degree of vacuum in the enclosure.

it is a further object of the invention to provide such a device which is simple in construction and does not necessitate an inconvenient conversion of the wall of the enclosure.

it is a further object of the invention to provide such a device which can easily be adapted to the requirements arising from the various conditions of treatment and operation in enclosures in which a very low pressure prevails.

The device according to the invention which comprises an auxiliary lowpressure compartment one end face of which receives the radiation which has passed through a partition pierced by a hole bringing the enclosure and the compartment into communication, is characterized in that the partition pierced by a hole is situated inside the enclosure.

According to a further feature of the invention, the end face of the compartment, opposite the partition, is equipped with an element which is sensitive to the radiation.

The pressure which prevails inside the compartment does not modify the pressure inside the enclosure to an appreciable extent because of the very small section of the hole.

In one embodiment, the volume of the compartment is sufficient, taking into consideration the anticipated duration of the operation, for the pressure inside said compartment, initially adjusted to a suitable value, to retain a sufficient value during the whole operation without its being necessary to admit a gas to counteract the incidence of molecules of condensable vapors-originating from the enclosure-on the sensitive element.

In another embodiment, a compartment of small dimensions is provided but connected to a chamber at the same pressure and larger in volume.

in yet another embodiment, having an extended use, provision is made for the continuous introduction into the compartment of a gas at a relatively low pressure but sufficient to prevent the incidence of molecules of condensable vapororiginating from the enclosure-on the sensitive element.

The sensitive element, which receives substantially no molecules of condensable vapor or of corrosive vapor, then supplies precise information thus permitting a changeover from quality supervision, which alone was possible hitherto, to quantity supervision.

With a device according to the invention, it is then possible to effect measurements which are comparable with one another, either in the course of one and the same operation or in the course of various operations taking place in one and the same apparatus, or even in the course of operations taking place in different apparatuses.

From the sensitive member, it is possible to control or monitor, during the whole period of an operation, the functioning of apparatuses placed in the enclosure under vacuum, particularly those which cause the appearance of the phenomenon producing radiation, thus affording the possibility of establishing a servocontrol.

According to another feature of the invention, the compartment of the device is partially inside the enclosure and partially outside it.

In another embodiment, the compartment is entirely inside the enclosure and can thus be brought close to the source of radiation.

The kinetic theory of gases renders it possible to determine, in known manner, the value required for the pressure inside the compartment, the length of the latter, that is to say the distance between the aperture of very small section and the sensitive member, as well as the diameter of the aperture, to ensure the total absence of condensable deposit on the sensitive member, taking into consideration the pumping means connected to the enclosure.

The sensitive member may be of any type. It may simply comprise a member sensitive to the radiation. It may also comprise an element sensitive to the radiation and preceded or followed by a suitable device.

' In the following description, given by way of example, reference is made to the accompanying drawing in which:

FIG. 1 is a diagrammatic view of a device according to the invention, for one form of construction;

FIG. 2 is a diagrammatic view of an embodiment of a treatment installation comprising a device according to the invention;

FIG. 3 is a diagrammatic view of an installation comprising a device according to the invention but in accordance with another embodiment;

FIG. 4 is a similar view of FIG. 2 but comprising a device like that in the embodiment illustrated in FIG. 3;

FIG. 5 is a rather more complete diagrammatic view of a treatment installation according to the invention in accordance with yet another embodiment;

FIG. 6 is a diagram of an installation according to the invention, with a servocontrol;

FIG. 7 is a partial view of an installation for another embodiment and illustrating pumping means;

FIG. 8 is a similar view but for another embodiment;

FIG. 9 is a view of an installation comprising a device according to the invention for yet another embodiment.

Reference will first be made to FIG. 1, relating to one embodiment of the device according to the invention. In this form of construction, the device according to the invention, 19, comprises a sensitive element 20, placed at the bottom of an elongated compartment 21 which, bounded b7 a lateral wall 22, may be generally cylindrical in shape. The compartment 21 is connected in a sealed manner to an enclosure 26, which is maintained under vacuum," that is to say at a very low pressure, and in which there is placed a substance being treated. The compartment 21 is directed towards said substance. The wall 23 of the compartment 21 opposite the sensitive element 20 is pierced by an aperture 24 of small diameter. Leading into the volume 28, inside the compartment 21, is a tube 25 by means of which there is maintained, inside the volume 28, a sufficient pressure for substantially none of the molecules of condensable vapor originating from a substance inside the enclosure 26, maintained under "vacuum," that is to say at a very low pressure, with which the compartment is in communication only through the aperture 24, to be able to reach the sensitive element 20.

The gas admitted through the tube 25 may, if necessary, be inert with respect to the substance being treated in the enclosure 26 and it is little or not at all absorbent with respect to the radiation to be analyzed for example that emanating from the substance being treated.

The pressure of the gas in the compartment 21 is selected in such a manner that the molecular free path, in the sense of the kinetic theory of gases, of a vapor molecule entering the compartment 21 through the aperture 24 is less than the distance between said aperture and the sensitive element 20. The number of molecules of vapor reaching the sensitive element or the like is thus considerably reduced until it has no influence on the properties of fidelity and sensitivity of said sensitive element with respect to the radiation emanating from the substance being treated. In these circumstances, the signal present at the output 27 of the sensitive element 20 supplies precise information regarding said radiation penetrating into the compartment 21 through the aperture 24, the disturbing influence of a condensable vapor on the sensitive element thus being eliminated.

Because of the very small section of the aperture 24, the compartment 21 may act as a camera obscura and permit the formation of the image on the sensitive element through the radiation of a specimen being treated or a portion thereof.

Likewise because of the very small diameter of the aperture through which the radiation passes, the pumping means which are provided for an enclosure without the device are sufficient to maintain the pressure required for the treatment in the atmosphere of the enclosure.

In certain cases, auxiliary devices may be provided to eliminate the gas introduced into the enclosure from the device.

In one form of construction of the device which has produced satisfactory results with an enclosure inside which there prevailed a pressure of 10" torr (or mm. of mercury), the compartment had a length of 70 mm., the aperture had a diameter of 0.3 mm., the pressure inside the compartment was 10' torr (or mm. ofmercury).

A device according to the invention may be used for various purposes according to the nature of the radiation-sensitive element which it comprises. The sensitive element may, for example, be a thermopile, or it may consist of photoelectric cells, photodiodes, thermistors, or it may consist of a pneumatic receiver with capacitive detection, or a difiraction crystal, or a photographic plate.

The device 19 according to the invention may be placed entirely inside the enclosure. In the form of construction shown in FIG. 1, the portion of the compartment 21 which comprises the aperture 24 is situated inside the enclosure and the other portion is outside the enclosure, the passage through the wall of the enclosure by the compartment 21 being sealed.

lnthe installation shown in FIG. 2, the device 19 is placed entirely inside the enclosure and carried by an ad hoc support (not illustrated) in the vicinity of a source S of radiation consisting, for example, of a metal raised to an elevated temperature; the influence ofthe condensable vapor or any other vapor on the conditions of propagation of the radiation between the source S and the radiation inlet of the device according to the invention is thus extremely small. In this case, the sensitive element may be that of a television camera affording a remote image of a substance being treated.

In the form of construction shown in FIG. 3, a plurality of diaphragms 30, 31, 32 are interposed between the aperture 24 for the admission of the radiation to the device according to the invention and the sensitive element 20. The apertures 34, 35, 36 in said diaphragms may increase in diameter from that closest to the aperture 24 to that closest to the sensitive element. These diaphragms counteract the effect of the multiple collisions to which a molecule of vapor may be subjected by the molecules of gas contained in the compartment and some of which may bring said molecule of vapor towards the sensitive element. Thus the diaphragms contribute to the protection of the sensitive element with respect to the molecules of condensable vapor originating from the enclosure.

FIG. 4 shows a similar arrangement, the device according to the invention being completely inside the enclosure 26 as in the installation shown in FIG. 2. The sealed passages 37 and 38 for the wires 39 and 40 constituting the output of the sensitive element are shown diagrammatically as is the sealed passage 41 for the tube 25 provided to maintain the pressure in the compartment of the device.

Reference will now be made to FIG. 5. In this form on construction, the device according to the invention 70 includes a spectrograph 71 and a sensitive element 72 consisting of a counter sensitive to X-rays. It is thus possible to analyze a complex X-radiation penetrating into the spectrograph 71. This assembly is placed behind a tube 73 which may contain apertured diaphragms, and the end 74 of said tube adjacent to the enclosure 83 is pierced by an aperture 75 which defines the field of the spectrograph. The transverse wall 76 which separates the tube 73 from the spectrograph 71 comprises a hole of very small section 77. The appropriate pressure is maintained inside the tube 73 by a gas, for example argon, which arrives through a pipe 78 leaving a source 79. The tube 73 is connected to a socket 80 on the wall 81 of the enclosure 83 by means of a joint 82 permitting the orientation of the device and hence aiming at the various points of the zone to be observed S. This may, for example, be the surface of a substance subjected to the action of an electron bombardment from an electron gun 85 and it is the X-radiation supplied by the substance which is received by the sensitive element 72 without any screen having had to be traversed.

In an embodiment which has produced satisfactory results, the aperture 75 had a diameter of a few tenths of a millimetre. The hole 77 connecting the atmosphere of the spectrograph 71 to the tube 73 was a few hundredths of a millimetre.

The very small dimensions of the aperture through which the radiation enters the device permits the mounting of a plurality of devices according to the invention on one and the same enclosure without disturbing the pressure or other parameters thereof. Thus, in the installation illustrated, a second device 90 is provided comprising, for example, an element which is sensitive to thermal radiation and which is placed inside the enclosure 83. The sensitive element may, for example, consist of one or more photodiodes. The output 91 of the device 90 is connected to an indicating device 92. A gas at a suitable pressure is admitted into the interior of the compartment 93 of the device 90 through a tube 94 from a reservoir 95. Cooling of the body of the compartment 93 is obtained by circulation of a fluid originating from another reservoir 97 and conveyed by a tube 96.

Reference will now be made to FIG. 6. In this installation the output of the device according to the invention, 100, comprising the sensitive element which receives the radiation supplied by the source S, is conveyed, after passing through an amplifier 101, to a regulating device 102 for regulating the energy supplied by a source of electrical energy 103 to a device 104 which is inside or outside the enclosure 105 and the action of which causes the radiation of the source S. The device 104 may, for example, be an electron gun, the beam of which is used to effect a weld between two metal parts. Thus the satisfactory course of a welding operation can be supervised, for example the temperature of the welding zone can be maintained at the desired values.

A similar installation may likewise be used for the production of an alloy.

The appropriate temperature for this production may be obtained by means of an electron gun or by any other means.

lt is also possible, by using a device according to the invention comprising radiation-sensitive elements, to establish a control which maintains a bath of metal at a constant level.

Reference will now be made to FIG. 7. in this modification, the sensitive element 110 is placed on the rear wall 111 of a compartment 112, of which the front wall 113 comprises a plurality of apertures 114, 1 15, 116, of very small dimensions. Diaphragms, distributed in a plurality of sets, for example two sets 117 and 118, are interposed between the sensitive element 110 and the wall 113. The sensitive element 110 can thus receive simultaneously radiant energy originating from a plurality of points of the source S situated in the enclosure 1 19.

ln the embodiment shown in FIG. 7, the vacuum is maintained inside the enclosure 119 by a primary pump 120 and a secondary pump 121 in known manner. The pressure required inside the compartment 112 is assured by the connection of said compartment to a device 123 through a tube 122.

Reference will now be made to FIG. 8. In this form of construction, between the enclosure 130, the atmosphere of which is at low pressure, and the device 131 according to the invention, there is interposed an intermediate chamber 132 which is separated from the enclosure 130 by a partition 133 comprising an aperture 134, the section of which is at least equal to that of the aperture 135 provided in the front wall 136 of the device 131. The chamber 132 is brought into communication with a secondary vacuum source 137.

Such an installation may be used to advantage when the pressure inside the enclosure 130 is particularly low (very high vacuum), that is to say less than 10 torr (or millimetres of mercury). The pressure inside the compartment of the device 131 may be of the order of 10 mm. of mercury. The pressure inside the chamber 132 may be of the order of 10 to 10 mm. of mercury, for example.

Reference will now be made to FIG. 9. in this installation, the source of radiation S consists of metal brought to a high temperature by electron bombardment originating from an electron gun 50. The body 51 of the compartment of the device according to the invention is connected to a socket 52 on the body of the enclosure 54 by means of a joint 53 permitting orientation of the body 51. Opposite the partition 56 pierced by an aperture of small section 57, there is placed the lens 59 of an optical device 60 which ensures a sealed closure of the compartment. Leading into the compartment is a pipe 61 leaving a distributor 62 which is fed from a reservoir 63 and which causes sufficient pressure to prevail in the compartment, for example by injection of gas at a constant rate, to prevent the incidence of molecules of condensable vaporfor example, metal-originating from the enclosure 54, on the lens 59. The joint device 53 permits observation of the various points of the source S. The observation may be continued as long as necessary, since no metal deposit is formed on the lens 59.

The optical device 60 or telescope permits enlargement of the area of the specimen or source S observed through the small aperture. For observation with a telescope, an aperture diameter is preferably selected in such a manner that diffraction does not reduce the separative power to an appreciable extent and that the amount of energy reaching the eye is sufficient.

For an ordinary thermal treatment device, an aperture having a diameter of about 1 mm. is appropriate. A pressure of 10" mm. of mercury for example may then be selected for the atmosphere of the compartment. With a distance of about 10 cm. between the aperture and the lens, only about 1 molecule out of 5X10" passing through the aperture 57 reaches the lens 59.

The delivery of gas from the compartment to the treatment enclosure is then low in comparison with the delivery of the usual pumps for enclosure pressures comprised between 10" and 10 mm. of mercury for example. In the example given, the delivery of the diffusion pump was 2,000 liters per second, the delivery of the compartment to the enclosure being a few hundred liters per second.

We claim:

1. A thermal treatment device comprising means defining an enclosure adapted to contain a radiation-emitting subject being treated, means associated with said enclosure for thermally treating said subject, means defining an associated closed compartment having a partition adjacent one end that is formed with a relatively small opening providing direct communication between said enclosure and compartment, said opening being located and providing for passage of radiation from the subject into and through said compartment, means for maintaining the interior of said enclosure at a relatively low subatmosphere pressure, means for maintaining the interior of said compartment at a higher subatmospheric pressure, and radiation-sensitive means within the compartment being such that for the value of the higher pressure in the compartment substantially all vapor originating in the enclosure during treatment is prevented from reaching said radiation-sensitive means.

2. A device as claimed in claim 1, wherein the compartment is housed entirely inside the enclosure.

3. The device defined in claim 1, wherein said compartment defining means is part of a radiation detecting and/0r measuring apparatus containing said radiation-sensitive means.

4. A device as claimed in claim 3, wherein the apparatus is an X-ray spectrograph which extends the compartment and is in communication therewith through an opening, the section of which is of the same order of magnitude as that of the hole in the partition.

5. A device as claimed in claim 1, wherein the partition is pierced by a plurality of radiation passage openings.

6. A device as claimed in claim 1, further comprising in the compartment, between the partition and the sensitive means, a plurality of diaphragms with aligned apertures of increasing section when passing from the partition towards said sensitive means.

7. The device defined in claim 1, wherein said partition is disposed inside said enclosure.

8. The device defined in claim 1, wherein said thermally treating means comprises an electron gun connected to said enclosure for bombarding said subject.

9. The device defined in claim 1, wherein for a given pressure level in said compartment the size of the partition opening and the distance between said opening and the radiationsensitive means are in predetermined relation.

10. The device defined in claim 1, wherein means is provided for introducing inert gas into said compartment to be maintained at said higher subatmospheric pressure.

11. The device defined in claim 1, wherein an apertured radiation passing intermediate chamber is provided between said enclosure and said compartment, and means is provided for maintaining the intermediate chamber at a subatmospheric pressure that is not higher than said enclosure pressure and is lower than said compartment pressure.

12. A thermal treatment installation comprising means defining an enclosure, means for maintaining said enclosure at a low subatmospheric pressure, apparatus associated with said enclosure for causing a radiation to be emitted from a subject under treatment inside said enclosure, means for controlling said apparatus, a low-pressure compartment maintained at a higher subatmospheric pressure substantially closed at one end by a partition located inside said enclosure, a relatively small opening in said partition for bringing said enclosure and said compartment into direct communication, and a radiation sensitive element operatively connected to said apparatus control means disposed in said compartment at its other end opposite and spaced apart from said one end, the section of the opening in said partition and the distance between said partition and said element being such that for a given value of the pressure in said compartment, substantially no vapor molecules originating from the treatment operation in the enclosure reach said element.

13. Aninstallation as claimed in claim 12, wherein said apparatus is an electron gun.

Patent No.

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(SPJAL) Attach:

mawmn M."Ln'lTCH EU IU WM UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,581,086 Dated may 25. 1971 Inventor) Bernard M. Daigne and Louis Pelletier It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

line 11, change "of" to -to-.

line 27 after "bounded" change "b7" to -by--. line 46, insert a gomma after "analyzed" line 3, change "lOi to -l0' line 6, change "10 to l0" line 50, change "on" to -of-.

line 62 change "10 to -l0" line 64, change "10 to -l0" line 65 change "10 to -lO' change "10 to -lO line 6, insert a comma after "vapo:

line 7, delete the comma after "example"; insert a comma after he dash.

line 21, change "10 to --1o' line 28, change "10 to --1oline 29, change "10 to --10' line 46, Claim 1 after "com artment" insert at the other end thereof for receiving said radiation, the size of the opening and the distance between the opening and the radiation sensitive means within the compartment line 59, Claim 4, change "hole" to -opening Signed and sealed this R th day of October 1971.

HOHMLRT GOT'ISGHALK Attnstinu orrinn iitih "cnmTnIaafianan ofTninm 1 

2. A device as claimed in claim 1, wherein the compartment is housed entirely inside the enclosure.
 3. The device defined in claim 1, wherein said compartment defining means is part of a radiation detecting and/or measuring apparatus containing said radiation-sensitive means.
 4. A device as claimed in claim 3, wherein the apparatus is an X-ray spectrograph which extends the compartment and is in communication therewith through an opening, the section of which is of the same order of magnitude as that of the hole in the partition.
 5. A device as claimed in claim 1, wherein the partition is pierced by a plurality of radiation passage openings.
 6. A device as claimed in claim 1, further comprising in the compartment, between the partition and the sensitive means, a plurality of diaphragms with aligned apertures of increasing section when passing from the partition towards said sensitive means.
 7. The device defined in claim 1, wherein said partition is disposed inside said enclosure.
 8. The device defined in claim 1, wherein said thermally treating means comprises an electron gun connected to said enclosure for bombarding said subject.
 9. The device defined in claim 1, wherein for a given pressure level in said compartment the size of the partition opening and the distance between said opening and the radiation-sensitive means are in predetermined relation.
 10. The device defined in claim 1, wherein means is provided for introducing inert gas into said compartment to be maintained at said higher subatmospheric pressure.
 11. The device defined in claim 1, wherein an apertured radiation passing intermediate chamber is provided between said enclosure and said compartment, and means is provided for maintaining the intermediate chamber at a subatmospheric pressure that is not higher than said enclosure pressure and is lower than said compartment pressure.
 12. A thermal treatment installation comprising means defining an enclosure, means for maintaining said enclosure at a low subatmospheric pressure, apparatus associated with said enclosure for causing a radiation to be emitted from a subject under treatment inside said enclosure, means for controlling said apparatus, a low-pressure compartment maintained at a higher subatmospheric pressure substantially closed at one end by a partition located inside said enclosure, a relatively small opening in said partition for bringing said enclosure and said compartment into direct communication, and a radiation sensitive element operatively connected to said apparatus control means disposed in said compartment at its other end opposite and spaced apart from said One end, the section of the opening in said partition and the distance between said partition and said element being such that for a given value of the pressure in said compartment, substantially no vapor molecules originating from the treatment operation in the enclosure reach said element.
 13. An installation as claimed in claim 12, wherein said apparatus is an electron gun. 